The present invention relates to a blade holder for a doctor, in which in the front part there is a throat or similar for attaching the doctor blade of the doctor and which is intended to be attached from its rear part to the frame by means of an attachment flange, and which blade holder has loading members connected to it to press the doctor blade against the surface to be doctored. The invention also relates to a method for using the doctor.
In conventional doctors, there are principally two kinds of blade holder. The first kind are fixed, i.e. rigid blade holders. The second kind, on the other hand, are flexible blade holders. The flexible blade holders can be further divided more precisely into flexible and profiling blade holders. Conventional profiling (flexible) doctors include a blade carrier with a blade holder fitted rotatably to it. Usually, the rotation is implemented by means of bearings, which extend from one end of the doctor to the other. In addition, a doctor blade is fitted to the blade holder, to doctor the surface of a roll or a similar moving surface. In order to alter the position of the doctor blade and to create an adequate blade load, the blade holder is rotated in relation to the blade carrier, by means of loading members. Normally, two loading hoses between the blade carrier and the blade holder, on each side of the bearings, are used as the loading members. Particularly in paper machines, there are numerous such doctors in several different positions. The doctor beam too, with its possible loading members, can also be used to create a basic load on the doctor blade. In rigid blade holders, it is precisely the doctor beam only that loads the doctor blade.
Mainly on account of the bearings, known doctor-blade-holder combinations are extremely complicated and thus also expensive. The bearings contain many moving parts, which wear in use and thus require maintenance. Looseness in the bearings may also have an adverse effect on the doctoring result. A fixed blade holder transmits all the force from the doctor beam to the surface of the roll being doctored. In this case, there is no way of compensating for force variations, installation faults, or similar caused by the bearings or other structures. Profiling and flexible blade holders in general can compensate slightly for these variations, so that the bearing system used in the blade holder is not quite so critical. On the other hand, looseness in the bearings and other structures in the blade holder will cause such detrimental variations. The blade angle of the doctor blade also changes as the doctor blade wears, hampering the operation of the doctor and shortening the doctor blade""s service life. In addition, metallic blade holders together with the other components add considerably to the total weight of the doctor. Service costs are further increased by the several different blade-holder models, each of which requires different spare-parts and tools.
The invention is intended to create a blade holder for a doctor, which contains fewer components than previous known blade holders and which is more economical to manufacture. The invention is also intended to achieve a method for using the doctor, which method is simpler to use and easier to control.
The characteristic features of this invention are provided by a blade holder for a doctor, in which in the front part there is a throat for attaching the doctor blade of the doctor and which is intended to be attached by its rear part to the frame by an attachment flange. The blade holder has loading members connected thereto to press the doctor blade against the surface to be doctored, and is characterized in that the blade holder further includes a relatively stiff, slightly flexible frame plate, which incorporates the attachment flange, and loading devices for directing the force of the loading members on the frame plate at a distance from the attachment flange, in order to bend the frame plate and thus press the doctor blade against the surface to be doctored.
The frame plate may be manufactured from a composite material to form a composite piece and reinforcing fibers of the composite piece are oriented in such a way, that the composite piece is relatively stiff in the lateral direction of the doctor blade and essentially flexible in the longitudinal direction of the doctor blade.
In one arrangement the loading members include one loading hose, which is set between the frame plate and the loading devices, in order to alter the distance between them. The loading devices include a backing plate, which is attached, by a connector at a distance from the frame plate, and the loading members are arranged to affect the distance between the rear parts of the frame plate and the backing plate. The loading members may include a protruding piece adapted to be attached to frame, which extends for a distance from the attachment flange, and in which space for the loading members is arranged.
A method for using a doctor, in which there is a throat in the front part of the blade holder of the doctor for attaching the doctor blade of the doctor and the blade holder is attached from its rear part to the frame by an attachment flange, and the blade holder has loading members connected to it, by means of which the doctor blade is pressed against the surface to be doctored, is characterized in that the blade holder is formed of a relatively stiff, slightly flexible plate forming a frame plate, which is bent by a force, which is directed at a distance from the attachment flange, so that a force pressing against the surface is created in the doctor blade. The force is transmitted with the aid of a stiff blacking plate from a rear part to a front part of the frame plate so that the stiff backing plate is attached by its front part to the frame plate and its rear part is at a distance from the frame plate determined by the loading members. Loading members are located at the end of the protruding piece attached to the attachment flange to act directly on the front part of the frame plate.
A blade holder according to the invention has no bearings or other moving parts at all, instead, the structural components are fitted, to each other. This substantially simplifies the construction of the blade holder. Sufficient movement is created in the doctor blade by means the flexing of the structural components, which is created by means of loading members. In addition, the properties of the blade holder can be adapted by means of the selection of the manufacturing materials. At the same time, the weight of the blade holder is reduced and there is greater freedom of design. The method according to the invention permits the accurate loading of the doctor in a simple, but comprehensive manner.
In the following, the invention is disclosed in detail with reference to the accompanying drawings showing some applications of the invention.